With some inspiration from the potential snow storm last week, I endeavored to test my emergency preparedness for heating my apartment when the power is out. I never did lose power, but the test was successful and I am happy to know that if I did lose power in the winter, I can keep warm at home.

I attached an inverter to a marine battery, then plugged in my Rinnai heater and it ran just fine. The Rinnai does buzz a bit loudly, but that's because the inverter does not produce a "true-sine-wave" signal. I tested the setup with a box-fan attached to the inverter as well and it worked fine.

With the fan and the heater both running on LOW the draw was 115W. Some quick and super dirty math approximations tell me that the battery (if fully charged) will run this about 11 hours. This would be longer if the box-fan isn’t running (less power would be used).

Since my previous post I have added a couple additional temperature sensors to my piHouse project. One is an outdoor temperature sensor that I previously programmed but never installed outside, and the other is a new sensor in my bedroom. This involved some hardware planning and effort installing because I had to run a cable through the house and outside, but once I tested the new cable run, it was relatively simple to duplicate the software for the sensors I already had.

The part of this that took the most time was pulling the cable and then soldering the connections. The biggest problem I have is placement of the outdoor sensor. I am having issues with direct Sunlight.

Here are some highlights, you can find the whole story here. This time I also include some examples of the commands I use on the raspberry pi to obtain the data.

When testing my hardware connections, I use this command to ask the pi to take a reading and then display the result to the command line:

It could use a little improvement if anyone is interested in forking it! It needs some testing with binary files. It needs a way to store the length of the message. And ideally, it'd use a pre-shared key (maybe?) to allow you both: A. define where the payload is hidden in the image, and B. actually encrypt the payload (which is, as of now, unencrypted). Which makes it so it doesn't follow Kerckhoff's Principle [wikipedia].

...Unfortunately every single message is decoded as "Drink more ovaltine" [youtube] (...just kidding. it'll do whatever payload you want)

I've been working on a Raspberry Pi project and got it running this weekend. This post is about the hardware and the installation. I will post later about how the code works.

Introduction

I have been using microcontrollers for a long time now. I started in college as part of the program and have never stopped. Professionally, educationally, hobby, I've done projects of all types.

Recently I decided to try something with a Raspberry Pi. It is the next step up, basically being a little computer. This was so I could play with Linux again (it's been years) and do something with a web browser. These are things I don't have experience with and have been interested in learning for some time.

The project I settled on was a monitor for the furnace in my apartment. This monitor will measure temperature(s) and sense if the furnace is running, then log this data. There will be a web interface that will draw graphs of the data on a daily basis. There will also be an LCD screen on the pi so that I can see the current data without needing a web browser.

Part 1: Hardware

The first step was to make sure I could sense whether the furnace was running. My furnace is controlled by a thermostat. A thermostat is a temperature controlled mechanical switch. Mine looks like this (The wire hanging down was added later):

I needed to open this up to see how it worked. So, I pulled off the ring on the front and exposed 3 screws holding it to the wall. I took out the screws and pulled the switch off the wall. I was left with a mounting plate that included a set of screw terminals with a 2 conductor wire attached. This is the wire running to the furnace in the basement that controls the furnace.

The screw terminals were labeled as RH and W. I took out my mult-meter and started doing some measuring.

This means that I need to monitor the voltage across terminals RH and W. If voltage is present, the furnace should be off. The 95mA is mostly unimportant because the thermostat is going to stay in place. I just need to make sure the pi doesn’t draw so much current that it turns on the furnace on it’s own. I drew up the below circuit to accomplish this using a rectifier circuit and an opto-isolator fed into GPIO24.

In this circuit, when the thermostat is open, the 10K resistor attached to the terminals limits the current feeding the 4 diodes, which function as a bridge-rectifier. This rectified AC then drives the LED of the opto-isolator. When the LED is lit, is turns on the transistor, shorting GPIO24 to GND with a 1uF cap for smoothing because its an AC signal. When the thermostat is closed, there is no current driving the opto-isolator and GPIO24 is pulled up to to 3.3V by a 100K resistor.

With the furnace monitoring designed, I had to decide on a temperature sensor. Unfortunately, the raspberry pi doesn’t have any built-in analog inputs. This was a little disappointing because it’s a standard feature on most microcontrollers I have used, however this is a computer. After a little research, I settled on a sensor that uses the Dallas 1-wire protocol. This is a serial bus that is similar to I2C. I liked it becuase there is pi support and since it is a bus, it is expandable (multiple sensors) without using more inputs. I found some DS18B20 1-wire Temperature Sensor ICs in a probe package with wire attached on Amazon, a bought a few.

Following the datasheet recommendations, I wired up the temp sensor like this:

The last piece for this was an LCD screen. I did some research and picked a product from Adafruit that has a 16X2 RGB LCD Screen and 5 buttons on a “shield” style board that plugs into the GPIO header on the pi. I ordered one and when it came in, I soldered it together.

After much programming (That will be a future post), I had all the parts working. So it was time to put the unit together. I plugged the LCD screen into the pi, then soldered some wires to the backside of the header-pins on the LCD shield. The other ends of the wires go to some proto-board where I built the schematics pictured above. I then added a 2-conductor wire in parallel to the thermostat and connected the other end to the pi’s “furnace” input. I wired up the Temperature sensor. I mounted it all to a bookshelf and fired it up.

Jesse unveiled the finished product in a previous post, and it does look awesome. Here are some photos and a simplified and incomplete account of how we got there. Disclosure, this took place off-campus of Laboratory B as we do not currently have the tools on-site.

This sign was created by etching a sheet of acrylic and then edge-lightning the result. The etching is basically a shallow cut that causes light in the material to reflect out. The cutting was accomplished using a computer numerical controlled (CNC) milling-machine.

First, we started with a high-res version of the Laboratory B Lightning Bolt (credit to Brenton). This was imported into a program called PartMaster and converted to a .dxf file. From this CAD file, we asked the computer (nicely) to generate G-code. G-code is what we needed to describe to the CNC machine how to move the cutting bit and etch the material. The CNC machine is controlled by a program called Mach3 CNC. This software reads text file containing the G-code and interfaces with the milling-machine to move the XY table and the drill head (Z) in order to accomplish the cut.

The milling-machine we used for this project was... a little too big. We wanted to use the whole 10" x 8" sheet so we used the big machine, but since it's not a router, it is normally used with R8 Collets.... the point is, the chuck we used to hold the etching bit was too short. You can see in this next photos that we couldn't reach the table and had to add some height to the mounting of the acrylic. Once this was done, we "zeroed" the machine. This is a process where we tell the Mach3 software what the location of the material to be cut is, so that it moves everything into the right place at the right time. Then we hit "START" and watched! Action shots follow, complete with my watching through my safety goggles.

I should have been grading lab reports, but instead I made this key holder with some Legos. I screwed some picture frame hooks into a few full-height blocks (2x4, 2x3, 1x4) and attached a large base to the wall. Put some key rings on the Legos, attach the Legos to the base, key holder. My favorite part is that I can add whatever creation I want to the base plate as long as it can sit vertical, which is always true because it's Legos. This is a simple spaceship I put together in a few seconds.

Thank you everyone who came and stopped by at our booth at Tech Jam! It was great to meet all of you and we hope to see you down at the space during open hours 6-8pm Tuesday or Thursday soon! Here are copies of the flyers from the table with instructions on making free calls included:

d00dz* do you rock out on IRC? If you don't... You're missing out on one of the pure joys of geekdom, one of the original forms of the hacker dungeon in cyberspace. And you don't have to be a rocket scientist / brain surgeon / Ada programmer / BIOS reverse engineer -- you just have to download an IRC client**, or use one on the web (which is even easier) and for server use irc.freenode.net, and then join #laboratoryb (you do know that the hashtag originated from IRC channels, right!?)

Then! You can make all the obnoxious prank calls you want with our friendly*** bot Whistler! He's our IRC robot who's hooked up to our Asterisk box at the lab, and he's got functionality which does a text-to-speech and originates a call to a phone number of your choosing to harangue your friends, foes, or send an "I love you" to your mom from a robot (moms love that, kinda?)

But, the best part is... He's open source! You can check out all his node.js code on Google Code. So if you want to, you can set up your own instance, or get your hands dirty and improve your skill with node.js by adding feature and improving him.

* And dud3773s, of course.** May I suggest irssi if you're a linux geek who likes the CLI, or Quassel if you're a GUI person (no shame, of course)*** He might mom joke you now and again, and we hope he hasn't become sentient.